1. Field of the Invention
The present invention relates to a thermally assisted magnetic recording head, and in particular relates to the configuration of a magnetic circuit used for recording.
2. Description of the Related Art
Recently, in a magnetic recording device typified by a magnetic disk apparatus, in association with high recording density, there is a demand for improvement in the performance of thin film magnetic heads and magnetic recording media. As the thin film magnetic head, composite type thin film magnetic heads are widely used in which a reproducing head having a magneto-resistive effect element (MR element) for reading, and a recording head having an induction-type electromagnetic transducer element for writing, are laminated on a substrate.
The magnetic recording medium is a discontinuous medium where magnetic grains are aggregated, and each magnetic grain has a single magnetic domain structure. Each recording bit on the magnetic recording medium is configured by a plurality of magnetic grains. In order to increase the recording density, asperities at a border between adjacent recording bits need to be decreased by decreasing the size of the magnetic grains. On the other hand, decreasing the size of the magnetic grains, i.e., decreasing in the volumes of the magnetic grains, results in a decrease in the thermal stability of magnetization in the magnetic grains. In order to resolve this problem, it is effective to increase the anisotropic energy of the magnetic grains. However, the greater anisotropic energy of the magnetic grains enhances the coercive force of the magnetic grains, making it difficult to record the information on an existing magnetic head.
As a method of resolving this problem, a so-called thermally assisted magnetic recording is proposed. In this method, a magnetic recording medium with a high coercive force can be used. At the time of recording information, the simultaneous addition of a magnetic field and heat to a portion of the recording medium where information is recorded increases the temperature of that portion. This results in information being recorded by the magnetic field at the portion where the coercive force is decreased. Hereafter, the magnetic head used for thermally assisted magnetic recording is referred to as a thermally assisted magnetic recording head.
In thermally assisted magnetic recording, near-field light (NF light) is used in general as a means for adding heat to the magnetic recording medium. The NF light is a type of electromagnetic field formed around a material, and is not restricted by a diffraction limit due to light wavelength. As a result, it is possible to focus light onto a very small domain on the order of tens of nm.
A thermally assisted magnetic recording head using a NF light generator is described in US2010/0103553. A magnetic circuit that applies a magnetic field to a magnetic recording medium extends with a roughly U-shaped form within a plane that is orthogonal to an air bearing surface (ABS) of the magnetic head and the substrate, a magnetic flux is emitted from one end of the U-shape, and the magnetic flux is absorbed from the other end. An NF light generator is positioned inside the U-shape within the plane, i.e., is positioned between both ends of the magnetic circuit when viewed in the track direction. As a result, the magnetic flux emitted from one end of the magnetic circuit passes through the NF light generator after entering into the magnetic recording medium, and is again absorbed by the magnetic circuit at the other end of the magnetic circuit.
In a conventional thermally assisted magnetic recording head having such a positional relationship between the NF light generator and the magnetic circuit, the below mentioned problem occurs. In order to efficiently perform magnetic recording on the magnetic recording medium, it is effective to enhance the effective magnetic gradient in the down track direction (recording medium circumferential direction). The effective magnetic gradient relies upon both the magnetic gradient in the down track direction formed by the magnetic circuit and the temperature gradient of the magnetic recording medium in the down track direction formed by the NF light generator. In a conventional thermally assisted magnetic recording head, although high magnetic field intensity is obtained between both ends of the magnetic circuit, fluctuation of the magnetic field intensity in the down track direction is not so great. Therefore, in the thermally assisted magnetic recording head where the NF light generator is positioned between both ends of the magnetic circuit, it is difficult to obtain a high magnetic gradient by the magnetic circuit in the vicinity where the NF light generator is positioned.
The objective of the present invention is to provide a thermally assisted magnetic recording head that can obtain a high magnetic gradient by a magnetic circuit in the vicinity where an NF light generator is positioned.